1) Field of the Disclosure
The disclosure relates generally to air conditioning systems and methods, and more particularly, to air conditioning systems and methods for pressurized aircraft that provide increased air conditioning system efficiency through reduction in power usage, as well as expanded air conditioning system capability at high aircraft speeds.
2) Description of Related Art
A primary function of aircraft air conditioning and thermal management systems is to transfer heat away from aircraft equipment, aircraft occupants, and aircraft interior compartments, such as the passenger cabin, cargo holds, and other interior compartments. In removing such heat, the aircraft air conditioning and thermal management systems typically require a heat sink to transfer the heat energy to. Possible heat sinks offering the capacity commensurate to the aircraft air conditioning and thermal management system's need may include ram air, aircraft surfaces (e.g., skin or structure), or fuel. As aircraft speed increases, the ram air and skin temperatures may also increase. Consequently, at higher speeds (in excess of Mach 1.0), such heat sinks may become less effective. Thus, known high speed or supersonic aircraft have used fuel as the heat sink during high speed operation.
However, recent regulatory requirements and industry focus associated with aircraft fuel tank flammability may make the use of fuel as a heat sink for these functions no longer viable or an optimal design solution. Given such limitations, air conditioning and pressurization of high speed commercial aircraft may become more challenging, and may result in added cost, complexity, weight, and inefficiency.
In addition, a primary function of an aircraft air conditioning system is to provide outside air for ventilation, pressurization, and thermal management. A significant amount of energy may be required to bring outside air into a pressurized aircraft during cruise, where ambient pressures are low. Some of this energy may be recovered as thrust via cabin outflow devices.
Aircraft air conditioning and pressurization systems are typically the largest continuous secondary power users on a commercial aircraft, with aircraft propulsion being the primary power user. Providing power for such aircraft air conditioning and pressurization systems, in addition to the other secondary power users, may prove to be a design challenge for propulsion engines (the power source) and secondary power load management controls. Aircraft secondary power may be extracted through pneumatic power (engine bleed air), electrical power (shaft driven generators), and hydraulic power (via shaft driven pumps, augmented by pneumatic driven pumps). However, such pneumatic and electrical power sources may have limits, and the extraction of power from such sources may need to be managed to ensure critical limits are not exceeded. Moreover, secondary power extraction limitations, whether pneumatic or electrical power, may result in inadequate cooling. Further, in order to improve engine efficiency and operability, secondary power extraction may be limited. As aircraft cooling demands increase beyond the levels that may be accommodated with available secondary power levels, the aircraft thermal environment may be degraded. Such aircraft cooling demands may not be satisfied with known aircraft architecture without additional secondary power. However, satisfying this need may adversely impact known aircraft systems.
Thus, as engine developments become more efficient and the available secondary power reduces, the use of cabin energy during flight may be beneficial in supplementing any power deficiencies. Accordingly, there is a need for an improved aircraft air conditioning system and method that provides advantages over known systems and methods.